Bright copper plating



United States Patent F BRIGHT COPPER PLATING John F. Beaver, Piqua, Ohio No-Drawing. Application July 18, 1955, Serial No. 522,839

20 Claims. (Cl. 204-52) This invention relates to electro-deposition of copper from aqueous acidic electrolyte solutions. The inventiondeals more particularly with bright copper plating, and wherein use is made of secondary addition agents which give a wider range of bright metal plating and a higher allowable current density without incurring detrimental efiects such as burning and treeing of the deposit.

It has been found, when copper plating with acid baths, that when certain selected secondary addition agents are added in small amounts to a bright or semibright acid copper plating bath containing, for example, a primary brightener such as thiourea or thiourea derivative, e. g., acetylthiourea or thiosemicarbazide and the like, as described in U. S. Patents Nos. 2,391,289; 2,602,- 774; and 2,696,467, the range of proportionate constituents which may be used to produce bright, smooth metal deposits is widened or increased without encountering the difliculties such as hereinbefore mentioned.

Accordingly, it is an object of this invention to provide a bright copper acid plating bath and method of electroplating copper from acid baths which is operable using a relatively wider range of concentration, current densities and voltage than has been possible heretofore.

Another object of the invention is to produce a bright copper deposit by electrolysis from an acidplating bath, wherein the plating operation can be carried out satisfactorily utilizing varied concentrations of constituents in the bath and current densities without noticeable deterioration of the bath or impairment of the coating.

It is another object of. the invention to provide a bright copper deposit by electrolysis and improved electrolyte bath which does not require frequent renewal of electrolyte.

Another object of the invention is to provide a bright copper plating electrolyte using an acid bath,- and where-- in addition agents are added in conjunction with conventional bright. copper producing agents to increase the efliciency of the plating bath and range of concentration in which the electrolyte is operative for plating bright copper deposits.

Another object of the invention is to provide a new and improved bath and process for electro-deposition of copper deposits having a high degree of luster and brightness and at the same time provide a bath having a relatively high throwing power.

The present invention broadly concerns the discovery that the addition of certain selected addition agents in small amounts to a bright copper plating bath permits the use of higher current densities and the production of smoother and improved deposits while at the same time permitting a wider variety of objects to be plated.

The new addition agents, which are conveniently referred to as secondary addition agents, are effective with or without the presence of such substances as molasses, lignin, dextrin, caramel, etc., and are particularly useful as addition agents, especially for plating baths that have been in operation for a period of several days, or weeks,

Patented Sept. 3, 1957 ice employed in conjunction with primary-brightening agents as aforementioned.

The novel compounds found useful as secondary addition agents are organic dyes,'and such as selected from one or more of the compounds hereinafter described, the same being used either singly or in combination, and wherein the total amount of the dyes added to the copper plating bath does not exceed a certain concentration. The compounds elfective contain at least one amino group.

The following are typical groups of the secondary addition agents which have been found effective, however, it is to 'be understood that these groups are typical and that-the invention is not to be specifically restrictedto these dyes or compounds alone. The compounds found particularly useful are as follows:

GROUP I X R1\ /R1 N- N 132 I \R2 N Cone, 0ptlgrams/ mum,

liter gramsl' liter (i1 1 (CHahN N(CH3)2 .0o2-.05 004-.01

Methylene Blue 01 l (CHmN M0113), .002-.05 .oo4-.o1

\N/ NE:

Toluldlne Blue 0 Cl l.

H'lN NHZ .002-.e5 .004-.01

Lauths Violet Z1 N 02 4 (CH3)2N N(CH3)1 .002.05 .004-.01

Methylene Green that the presence of other radicals substituted for hydrogen on the nucleus, such as in Examples 2 and 4,

while changing the color of the compound does not efiect the beneficial results obtained.

The second group of compounds which have been found to be particularly useful as secondary addition agents are identical with Group I compounds except that the S atom in the nucleusris replaced by 0. Such compounds are known as oxazine dyes and typical groups are wherein R1 and R2 are radicals selected from the group of hydrogen, methyl, ethyl, and phenyl radicals and X rs an anion, such as halide, sulfate or nitrate and other anions which are compatible in the plating bath.

00110., Optigramsl mum,

liter grams] liter 1 (CHs)zN- N(OH3) .002-.05 004-. 015 p Capri Blue 2 HrN N(CzH )n 002-. 05 004-. 015

Nile Blue El 3..- N(CHs)2 .002.05 .0041 015 To further illustrate specific examples of electrolyte baths found useful for copper plating in accordance with this invention, the following are typical and illustrative, and in which the described quantities of the constituents are present per liter of aqueous solution.

Methylene Blue The bath had a temperature of 85 F. Agitation was carried out by blowing air through the bath. The electric -current had a density of 100 amps. per sq. ft. and a voltage of 4.5 volts. The coating obtained in this instance was smooth and uniform and had a high luster.

Example 2 Gr./l. Copper sulfate 200 Sulfuric acid Chloride anion 0.005 Caramel and/or molasses 0.10 Acetyl thiourea 0.03 Sodium lauryl sulfate 0.10 Capri Blue 0.01

The process with this electrolyte was carried out under the same conditions as were used in connection with Example l, with the exception that agitation of the electrolyte was effected by moving the cathode instead of introducing air. The same favorable results were obtained.

Example 3 Gr./l. Copper sulfate 240 Sulfuric acid Thiourea 0.01 Dextrin 0.05 Toluidine Blue 0.01

Example 4 Same as Example 3, except that thiosemicarbazide is used in lieu of thiourea.

Example 5 Same as Example 3, except that acetyl thiourea is used in lieu of thiourea.

Example 6 Same as Example 3, except that Lauths Violet is used in place of Toluidine Blue.

Example 7 Same as Example 3, except that Methylene Green is used in place of Toluidine Blue.

Example 8 Example 9 Same as Example 3, except that Nile Blue A (e. g. Gr.

II (2)) is used in place of Toluidine Blue.

Example 10 Same as Example 3, except that 0.01 to .04 gm./l. of a wetting agent, e. g. alkali metal lauryl sulfate is added.

It is also found beneficial to employ a bath containing the chloride anion, preferably being maintained Within a range of about 0.001 to 0.020 grams per liter of electrolyte. The presence of lower or higher amounts of the chloride anion, however, does not produce the beneficial plating results, so that the copper deposit is less bright and not as smooth and even textured. f

It is also advantageous, though optional, to add an agent which acts as -a carrier for the primary brightener. Dextrin, molasses and caramel are excellent for this purpose. Further, in some instances it is also desirable to add a Wetting agent; sodium lauryl sulfate and sodium octyl sulfate are preferred therefor.

The articles to be plated are advantageously subjected to a preliminary treatment prior to the coating proper. For this purpose they are cleaned with an alkaline cleaner, dipped into acid in order to remove any rust, neutralized and then rinsed in water. It is also preferable to first apply a thin copper coating from a cyanide bath. Such a bath may contain from 3 to 5 ounces of copper metal per gallon, 1 /5: to 3 ounces of free sodium cyanide and from 2 tov 8. ounces of sodium carbonate. .Plating with this bath for from 3 to 4 minutes is sufiicient. After this hash plating the article is washed to remove the cyanide.

It is further advantageous to agitate the electrolyte during electrolysis. This may be carried out either by moving the cathode or by stirring the electrolyte, the latter being preferred. In particular has it been found satisfactory to efiect stirring -by blowing air through the bath. If stirring is carried out this way, however, it is advisable to restrict the quantity of the wetting agent to a minimum or omit it entirely, because otherwise excessive foaming takes place which impairs the operation.

The utilization of the secondary addition agent permits bright copper plating using bath temperatures and current densities of wider range than has been permitted heretofore, the same may be varied considerably, satisfactory deposits maybe obtained at bath temperatures of between about 60 F.140 F. When operating with large commercial production operation, it maybe preferred to maintain the electrolyte bath ator near room temperature, for example between about 85'95 F. Electric current densities may be varied over a range between about 5*250 amps. per square foot of cathode area. Higher current densities require increased agitation of the solution. The agitation may be accomplished by bubbling air through the electrolyte solution or by rapid movement of the cathode or circulating the electrolyte.

The baths described produce plating deposits of copper or chiefly of copper, which are bright and smooth. Employing the secondary addition agents in conjunction with the usual primary added agents produces bright deposits even if the conditions are not so accurately maintained as was heretofore required where only primary addition agents are used. The plating deposits are characterized by extreme fineness of metal structure and the production of a brilliant, smooth-copper plating which does not require buffing.

The bright copper plated articles produced according to this process may be readily electroplated with other metal such as bright nickel, chromium or the like, as desired, to form a final bright plate which requires little or no bufiing. This is particularly advantageous inasmuch as bufling removes a portion of the plate and endangers the cutting through of a thin plate. This, of course, is entirely eliminated by utilizing the present invention.

While certain embodiments of the electrolyte bath have been set forth as specific embodiments of my invention it is not intended thereby to limit the invention to the specific examples and details given in view of the fact that the invention is susceptible to various changes and modifications, particularly as to the concentration and current" densities for producing a bright metal deposit. Such modifications and changes are intended to come within the spirit and scope of this invention, and which,are more particularly set forth in the appended claims.

What is claimed is 1. In a method of electro-depositing copper from an aqueous copper sulfate-sulfuric acid bath, the step which comprises electrolyzing said aqueous acid copper bath containing a brightener compound which widens the range of solution concentration and electric current densities wherein plating can be conducted Without encountering burning and forming treeing deposits, said brightener compound comprising a thiazine dye having the general structural formula Rz\ i /Ri N N 112 i Ri N wherein Rr and R2 are radicals selected from the group consisting of hydrogen, methyl, ethyl, and phenyl rad icals and X is an anion compatible in the plating bath, said brightener being present in a minor proportion.

2.'In a method of electro-depositing copper from a aqueous copper sulfate-sulfuric acid bath, the step which comprises electrolyzing said aqueous acid copper bath containing a minor proportion of a brightener compound whichwidens the range of solution concentration and electric current densities wherein plating can be conducted without encountering burning and forming treeing deposits, said brightener compound being selected from the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue and Nile Blue, and mixturesthereof.

3. In a method of electro-depositing copper from an aqueous copper sulfate-sulfuric acid'bath, the step which comprises electrolyzing said aqueous acid copper bath containing a minor proportion of a brightener compound which widens the range of solution concentration and electric current densities wherein plating can be conducted without encountering burning and forming treeing deposits, said brightener compound being selected from the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue and Nile Blue, and mixtures thereof, said brightener being present in the bath in an amount of'between about 0.002 and 0.05 gm./l. of'electrolyte solution.

4. An aqueous copper sulfate-sulfuric iacid bath for electro-deposition of copper whichcontains a grain refining addition; agent,'said grain'refining agent comprising athiazine dye' which is. present in the amount of about 0.002to' 0.05 grarns per liter of said bath, said dyejbeing selected 'fr om the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue, Nile Blue, and mixtures thereof.

5. Anaqueou's coppersulfate-sulfuric acid bath for electro-deposition of copper which contains a grain refining addition agent, said grain refining agent being present in a minor proportion and'consis'ting of a compound having the structure selected from the group consisting of and wherein R1 and'R'z are radicals selected from the group consisting of hydrogen, methyl, ethyl, and phenyl radicals and X is an anion compatible in the plating bath.

6. In a method of elec-tro-depositing copper from an aqueous copper sulfate-sulfuric acid bath, said acid bath containing chloride anion within a range of about 0.001 to 0.02 gr./l. of the bath, the step which comprises electrolyzing said'aqueous. acid copper bath containing a minor proportion of a brightener compound which Widens the rangeof solution concentration and electric current densities wherein plating can be conducted without encountering burning and forming treeing deposits, said. brightener compound being selected from the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue and Nile Blue, and mixtures thereof.

7. An aqueous copper sulfate-sulfuric acid bath for electro-deposition of copper which contains a grain refining addition agent, said grain refining agent comprising a thiazine dye which is present in the amount of about 0.002 to 0.05 grams per liter of said hath, said acid bath containing chloride anion within a range of about 0.001

' to 0.02 grams per liter of the bath, said dye being selected from the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue, Nile Blue, and mixtures thereof.

8. In a method of electro-depositing copper from an aqueous copper sulfate-sulfuric acid bath, the step which comprises electrolyzing said aqueous acid copper bath containing a minor proportion of a brightener compound which widens the range of solution concentration and electric current densities wherein plating can be conducted without encountering burning and forming treeing deposits, said brightener compound comprising an oxazine dye having the general structural formula ene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue, Nile Blue, and mixtures thereof.

a 10. An aqueous copper sulfate sulfuric acid bath for electro-deposition of copper which contains a grain refining addition agent, said grainrefining agent comprising an oxazine dye which is present'in the amount of about 0.002 to 0.05 grams perliter of said bath, said acid bath containing chloride anion within a range of about 0.001 to 0.02 grams per liter of the bath, said dye being selected from the group consisting of Methylene Blue, Toluidine Blue, Lauths Violet, Methylene Green, Capri Blue, Nile Blue, and mixtures thereof.

11. In a method of electro-depositing copper from an aqueous copper sulfate-sulfuric acid bath, the step which comprises electrolyzing said aqueous acid copper bath containing a minor proportion of a brightener compound which widens the range of solution concentration and electric current densities wherein plating can be conducted without encountering burning and forming treeing deposits, said brightener compound having the structural formula 'Which widens therangeof solution concentration and electric current densities wherein plating can be conducted without encountering bu rningand forming treeing deposits, said brightenercompound having the structural formula V a where R is selected from the group consisting of methyl and ethyl, and X is a halogen.

13. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound selected from the group consisting of a thiazine dye and oxazine dye.

14. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound having the structural formula where R is selected from the group consisting of methyl and ethyl, and X is a halogen.

15. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound having the structural formula wherein R is selected from the group consisting of methyl and ethyl, and X is a halogen.

16. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains a minor proportion of an addition agent comprising an oxazine compound which contains at least one amino group, said dye being selected from the group consisting of Methylene Blue,

17. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound having the structural formula V (g1 (GH5)2N N 1): 7

N/ NH] 18. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound having the structural 19. An aqueous copper sulfate-sulfuric acid bath for electroplating copper which contains as an addition agent a minor proportion of a compound having the structural formula nemone, N

20. An aqueous copper sulfate sulfuric acidbath for electroplating copper which contains as an additlon agent a minor proportion of a compound having the structural References Cited in the filc of this patent formula UNITED STATES PATENTS 2,238,861 Lind ct a1. Apr. 15, 1941 o 5 2,291,590 Lind et a1. July 28, 1942 2 663 684 Pierce Dec. 22 1953 H 9 a MC 2,707,167 Hoover Apr. 26', 1955 

1. IN A METHOD OF ELECTRO-DEPOSITING COPPER FROM AN AQUEOUS COPPER SULFATE-SULFURIC ACID BATH, THE STEP WHICH COMPRISES ELECTROLYZING SAID AQUEOUS ACID COPPER BATH CONTAINING A BRIGHTENER COMPOUND WHICH WIDENS THE RANGE OF SOLUTION CONCENTRATION AND ELECTRIC CURRENT DENSITIES WHEREIN PLATING CAN BE CONDUCTED WITHOUT ENCOUNTERING BURNING AND FORMING TREEING DEPOSITS, SAID BRIGHTENER COMPOUND COMPRISING A THIAZINE DYE HAVING THE GENERAL STRUCTURAL FORMULA 